1. Field of the Invention
The present invention relates generally to liquid crystal display devices, and particularly, to a novel, low-cost, energy-efficient liquid crystal display device implementing dye impregnated photoluminescent fibers.
2. Discussion of the Prior Art
Current liquid crystal display devices employing white fluorescent backlight, with diffusers, color filters and a combination of a polarizer and analyzer, result in a luminous throughput efficiency of 5% or less. As liquid crystal display pixels become smaller, the aperture ratio (the open area of the pixel relative to the total pixel area) becomes smaller because the footprint size of the thin-film transistor (TFT) device can not be reduced proportionately. Further, the fabrication process for making the color filter is complicated and increases the cost of the display.
FIG. 1 is a schematic illustration depicting a pixel 12 of a conventional full-color LCD panel. The pixel 12 has three liquid crystal cells, which corresponds to red, green and blue cells. As shown in FIG. 1, the panel includes an optical guide 27, which guides white backlight 28 from a fluorescent lamp (not shown) through a polarizer 26, transparent electrodes 25a-25c, liquid crystal material 24, a transparent electrode 23, and red, green and blue color filters 20, 21 and 22, respectively.
Colored light is finally emitted through a glass substrate 19 and an analyzer 18. The polarization directions of polarizer 26 and analyzer 18 are aligned to obtain the designed contrast. It is understood that a diffuser element (not shown) may be placed on the light guide 27 for distributing transmitted light uniformly through the panel. A prism sheet (or a pair of prism sheets) additionally may bring the scattered light towards normal direction. It is understood that a liquid crystal cell additionally is comprised of TFT arrays and transparent electrodes (preferably comprised of Indium Tin-Oxide "ITO").
Even in the ideal case, white visible light utilizes only 1/3 of the incident light for this configuration because of the red, green and blue color filters. Moreover, the fabrication process to make these color filters requires exacting optical lithography technology, which increases the panel cost and the manufacturing time.
Color conversion utilizing photoluminescence phenomena have been described in the prior art. For instance, the references entitled "Incorporation of Photoluminescent Polarizers into Liquid Crystal Displays," Science 279, 835 (1998) by C. Weder, C. Sarwa, A. Montali, C. Bastiaansen, P. Smith, and "Polarizing Energy Transfer in Photoluminescent Materials for Display Applications," Nature, 392, 261 (1998) by A. Montali, C. Bastiaansen, P. Smith, C. Weder, each describe a new type of liquid crystal display implementing a photoluminescent sheet with polarized emission. Although the devices described in these references address the prior art limitations of the conventional device, the devices are not full color devices, and only a single or two color device can be achieved.
According to the display devices implementing photoluminescence as described in these references, a fluorescent dye absorbs the incident light and either re-emits a different color of a longer wavelength or transfers the energy to a second dye which then re-emits a different color of a longer wavelength. For instance, in the above-mentioned reference entitled "Polarizing Energy Transfer in Photoluminescent Materials for Display Applications," the ultraviolet (UV) light from the backlight is absorbed by a dye material DMC (Coumarin 1), and the energy is transferred to a stretch-aligned conjugated polymer material, EHO-OPPE, which re-emits polarized green light. When a sheet of this dye/polymer blend is placed in a liquid crystal display device it replaces both a polarizer and green color filter. This reference however, does not describe how to make a full color liquid crystal display.
It would be highly desirable to provide a full color liquid crystal display without the need for color filters and a polarizer, and further, a full color liquid crystal display that is highly efficient and can be manufactured using very low cost fabrication methods.